FIG. 1 shows a superhard component 100 that is insertable within a downhole tool (not shown) in accordance with an exemplary embodiment of the invention. One example of a superhard component 100 is a cutting element 100, or cutter, for rock bits. The cutting element 100 typically includes a substrate 110 having a contact face 115 and a cutting table 120. The cutting table 120 is fabricated using an ultra hard layer which is bonded to the contact face 115 by a sintering process. The substrate 110 is generally made from tungsten carbide-cobalt, or tungsten carbide, while the cutting table 120 is formed using a polycrystalline ultra hard material layer, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”), or tungsten carbide mixed with diamond crystals (impregnated segments). These cutting elements 100 are fabricated according to processes and materials known to persons having ordinary skill in the art. The cutting element 100 is referred to as a polycrystalline diamond compact (“PDC”) cutter when PCD is used to form the cutting table 120. PDC cutters are known for their toughness and durability, which allow them to be an effective cutting insert in demanding applications. Although one type of superhard component 100 has been described, other types of superhard components 100 can be utilized.
Common problems associated with these cutters 100 include chipping, spalling, partial fracturing, cracking, and/or flaking of the cutting table 120. These problems result in the early failure of the cutting table 120. Typically, high magnitude stresses generated on the cutting table 120 at the region where the cutting table 120 makes contact with earthen formations during drilling can cause these problems. These problems increase the cost of drilling due to costs associated with repair, production downtime, and labor costs. For these reasons, testing methods have been developed to ascertain the abrasion resistance and/or impact resistance of cutters 100 so that improved cutter longevity is achieved and the problems mentioned above are substantially reduced.
Superhard components 100, which include PDC cutters 100, have been tested for abrasive wear resistance through the use of two conventional testing methods. Early in the development of PDC materials, the abrasive wear resistance was tested using a conventional granite log test, which is described in further detail with respect to FIG. 2. However, as the PDC cutters 100 became more wear resistant and too much time and conventional target cylinders 250 (FIG. 2) were required to complete the conventional granite log test, the conventional vertical turret lathe (“VTL”) test, which is described in further detail with respect to FIG. 3, replaced the conventional granite log test for testing abrasive wear resistance.
FIG. 2 shows a lathe 200 for testing abrasive wear resistance of a superhard component 100 using a conventional granite log test. Although one exemplary apparatus configuration for the lathe 200 is provided, other apparatus configurations can be used without departing from the scope and spirit of the exemplary embodiment. Referring to FIG. 2, the lathe 200 includes a chuck 210, a tailstock 220, and a tool post 230 positioned between the chuck 210 and the tailstock 220. A conventional target cylinder 250 has a first end 252, a second end 254, and a sidewall 258 extending from the first end 252 to the second end 254. According to the conventional granite log test, sidewall 258 is an exposed surface 259 which makes contact with the superhard component 100 during the test. The first end 252 is coupled to the chuck 210, while the second end 254 is coupled to the tailstock 220. The chuck 210 is configured to rotate, thereby causing the conventional target cylinder 250 to also rotate along a central axis 256 of the conventional target cylinder 250. The tailstock 220 is configured to hold the second end 254 in place while the conventional target cylinder 250 rotates. The conventional target cylinder 250 is fabricated from a single uniform material, which is typically a natural rock type, such as granite, or concrete. Other single uniform rock types have been used for the conventional target cylinder 250, which includes, but is not limited to, Jackfork sandstone, Indiana limestone, Berea sandstone, Carthage marble, Champlain black marble, Berkley granite, Sierra white granite, Texas pink granite, and Georgia gray granite. The conventional target cylinder 250 has a compressive strength of about 25,000 pounds per square inch (“psi”) or less and an abrasiveness of about 6 CAI or less when natural rock types are used. These conventional target cylinders 250 fabricated from natural rock types are costly to acquire, shape, ship, and handle. The conventional target cylinder 250 has a compressive strength of about 12,000 psi or less and an abrasiveness of about 2 CAI or less when concrete is used.
The PDC cutter 100 is fitted to the lathe's tool post 230 so that the PDC cutter's cutting table 120 makes contact with the conventional target cylinder's exposed surface 259 and drawn back and forth across the exposed surface 259. The tool post 230 has an inward feed rate on the conventional target cylinder 250. The abrasive wear resistance for the PDC cutter 100 is determined as a wear ratio, which is defined as the volume of conventional target cylinder 250 that is removed to the volume of the PDC cutter's cutting table 120 that is removed. This wear ratio can be referred to as a grinding ratio (“G-Ratio”). Common values of the G-Ratio range from about 1,000,000/1 to 15,000,000/1 depending on the abrasiveness of the conventional target cylinder and the PDC cutter. Alternatively, instead of measuring volume of rock removed, the distance that the PDC cutter 100 travels across the conventional target cylinder 250 can be measured and used to quantify the abrasive wear resistance for the PDC cutter 100. Common values of the travelling distance range from about 15,000 feet to about 160,000 feet depending on the abrasiveness of the conventional target cylinder and the PDC cutter. Alternatively, other methods known to persons having ordinary skill in the art can be used to determine the wear resistance using the conventional granite log test. Operation and construction of the lathe 200 is known to people having ordinary skill in the art. Descriptions of this type of test is found in the Eaton, B. A., Bower, Jr., A. B., and Martis, J. A. “Manufactured Diamond Cutters Used In Drilling Bits.” Journal of Petroleum Technology, May 1975, 543-551. Society of Petroleum Engineers paper 5074-PA, which was published in the Journal of Petroleum Technology in May 1975, and also found in Maurer, William C., Advanced Drilling Techniques, Chapter 22, The Petroleum Publishing Company, 1980, pp. 541-591, which is incorporated by reference herein.
As previously mentioned, this conventional granite log test was adequate during the initial stages of PDC cutter 100 development. However, PDC cutters 100 have become more resistant to abrasive wear as the technology for PDC cutters 100 improved. Current technology PDC cutters 100 are capable of cutting through many conventional target cylinders 250 without ever developing any appreciable and measurable wear flat; thereby, making the conventional granite log test method inefficient and too costly for measuring the abrasive wear resistance of superhard components 100.
FIG. 3 shows a vertical turret lathe 300 for testing abrasive wear resistance of a superhard component 100 using a conventional vertical turret lathe (“VTL”) test. Although one exemplary apparatus configuration for the VTL 300 is provided, other apparatus configurations can be used without departing from the scope and spirit of the exemplary embodiment. The vertical turret lathe 300 includes a rotating table 310 and a tool holder 320 positioned above the rotating table 310. A conventional target cylinder 350 has a first end 352, a second end 354, and a sidewall 358 extending from the first end 352 to the second end 354. According to the conventional VTL test, second end 354 is an exposed surface 359 which makes contact with a superhard component's cutting table 120 during the test. The conventional target cylinder 350 is typically about thirty inches to about sixty inches in diameter, but can be smaller or larger depending upon the testing requirements. The conventional target cylinder 350 is typically larger in diameter than the conventional target cylinder 250 (FIG. 2).
The first end 352 is mounted on the lower rotating table 310 of the VTL 300, thereby having the exposed surface 359 face the tool holder 320. The PDC cutter 100 is mounted in the tool holder 320 above the conventional target cylinder's exposed surface 359 and makes contact with the exposed surface 359. The conventional target cylinder 350 is rotated via the rotating table 310 as the tool holder 320 cycles the PDC cutter 100 from the center of the conventional target cylinder's exposed surface 359 out to its edge and back again to the center of the conventional target cylinder's exposed surface 359. The tool holder 320 has a predetermined downward feed rate.
The VTL 300 is generally a larger machine when compared to the lathe 200 (FIG. 2) used for the conventional granite log test. The conventional VTL test allows for larger depths of cut to be made in the conventional target cylinder 350 and for the use of a larger conventional target cylinder 350 when compared to the depths of cut made and the size of the conventional target cylinder 250 (FIG. 2) used in the conventional granite log test. The capability of having larger depths of cut allows for higher loads to be placed on the PDC cutter 100. Additionally, the larger conventional target cylinder 350 provides for a greater rock volume for the PDC cutter 100 to act on and hence a longer duration for conducting the test on the same conventional target cylinder 350. Thus, fewer conventional target cylinders 350 are used when performing the conventional VTL test when compared to the number of conventional target cylinders 250 (FIG. 2) that are used in the conventional granite log test. The conventional target cylinder 350 is typically fabricated entirely from granite; however, the conventional target cylinder can be fabricated entirely from another single uniform natural material that includes, but is not limited to, Jackfork sandstone, Indiana limestone, Berea sandstone, Carthage marble, Champlain black marble, Berkley granite, Sierra white granite, Texas pink granite, and Georgia gray granite, or concrete. The conventional target cylinder 350 has a compressive strength of about 25,000 psi or less and an abrasiveness of about 6 CAI or less when natural rock types are used. As previously mentioned, these conventional target cylinders 350 fabricated from natural rock types are costly to acquire, shape, ship, and handle. The conventional target cylinder 350 has a compressive strength of about 12,000 psi or less and an abrasiveness of about 2 CAI or less when concrete is used. The abrasive wear resistance for the PDC cutter 100 is determined as a wear ratio, which is defined as the volume of conventional target cylinder 350 that is removed to the volume of the PDC cutter 100 that is removed. This wear ratio can be referred to as a grinding ratio (“G-Ratio”). Common values of the G-Ratio range from about 1,000,000/1 to about 15,000,000/1 depending on the abrasiveness of the conventional target cylinder and the PDC cutter. Alternatively, instead of measuring volume of rock removed, the distance that the PDC cutter 100 travels across the conventional target cylinder 350 can be measured and used to quantify the abrasive wear resistance for the PDC cutter 100. Common values of the travelling distance range from about 15,000 feet to about 160,000 feet depending one the abrasiveness of the conventional target cylinder and the PDC cutter.
Referring back to FIGS. 2 and 3, the conventional target cylinders 250 and 350 have limitations due to the material compositions used in fabricating the conventional target cylinders 250 and 350, which is either a natural material or concrete. When using a natural material, the material must be mined and shaped before the natural material becomes suitable for use as a conventional target cylinder 250 and 350. Additionally, certain provisions are to be made when using these natural materials due to their variability in properties. For instance, once a natural material is selected for use as the conventional target cylinder 250 and 350, additional natural material must be selected from the same mine to avoid expensive recalibration of the test. The same natural material from a different mine is likely to have different properties and thus result in testing discrepancies. Further, shipping costs, limited supplies of natural material, and natural variations all increase the cost and ability to obtain repeatable test results.
Concrete, however, has some advantages over natural material when fabricating the conventional target cylinders 250 and 350. Concrete is widely available and relatively inexpensive when compared to natural materials. Concrete is fabricated using local materials hence reducing transportation costs. Although concrete has some advantages over natural materials, concrete also has several disadvantages. According to one disadvantage, concrete has a much lower compressive strength when compared to rock strength found in the field. Conventional concrete has a typical compressive strength of about three kilo-pounds per square inch (“kpsi”), while some specialty concretes can reach about twelve to kpsi. However, rock strength found in the field typically ranges in compressive strength from about twenty kpsi to about sixty kpsi. Thus, the tests performed using concrete-formed conventional target cylinders 250 and 350 are not indicative of field results. According to another disadvantage, fabricating concrete is a much longer time consuming process. Concrete is typically cured for about twenty-eight days so that its specified strength is reliably reached. As known to people having ordinary skill in the art, a long fabrication duration for preparing the conventional target cylinder 250 and 350 becomes very expensive due to loss of time.
The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.